PASADENA – Roaming bands of mischievous Caltech students wreaked havoc all over campus Friday as part of the school’s annual “Ditch Day.”

Hardly anti-establishment – Ditch Day is cheerfully sanctioned by the school – the event allows graduating seniors to set up elaborate pranks and challenges, nicknamed “stacks,” designed originally to keep younger students from entering and “rearranging” seniors’ rooms.

“The underclassmen have to solve the pranks,” Caltech spokesman Jon Weiner explained. “They’re on a quest.”

Quests depend on which themes students choose to follow and often include pranks that require significant engineering prowess to pull off.

Senior Abraham Buditama, 21, built a challenge he called “Human Tetris” in the style of a popular Japanese game show challenge.

The device rolled along a homemade track and had a cardboard wall with cut-out shapes. Challengers had to contort their bodies to fit through the holes as the wall came toward them or get knocked down into a makeshift pit.

“The have to go through the hole or be smacked into the tarp covered with flour,” Buditama said.

One of the more impressive challenges was a 15-foot high wall of ice that students built and climbed using harnesses, ice axes and heavy boots with metal spikes.

“None of us have done this before so it was difficult but it was also a lot of fun,” 18-year-old freshman Wesley Swank said.

Many team themes ranged from the video game-related, such as Super Mario Brothers, to the science fiction-inspired, including Star Wars, and didn’t necessitate much math and science know-how.

Junior Eduardo Gonzalez had a bandage under his eye following a wooden-sword fight with other members of his team, based on the Nintendo game “The Legend of Zelda.”

His teammate, Jennifer Greco, explained that the Zelda squad’s next move involved “feeding something to Jabu-Jabu and rescuing the princess.”

Then there were themes that didn’t seem to take much thought at all.

One team simply referred to itself as “Beer Room.”

Carousing Beer Room members wandered around campus with a boombox blaring and said their team was meant to be a mild protest against the school closing a popular drinking facility on campus.

Students showed their displeasure by engaging in challenges like “going to the pool” and “chugging energy drinks.”